Fourth Recess Lake is a gorgeous blue lake sitting in the Pioneer Basin. Vertical granite cliffs surround the lake, with a waterfall at the headwall above it. From Mono Pass, the trail goes mostly down the valley, passing by Upper Trail Lake. This is a challenging full-day hike that should be well-planned, and it can also be done as a multi-day trip. It is good to have trekking poles and hiking boots and be aware of altitude sickness when crossing the pass.
Getting to this isolated lake will surely pay off the effort, and you might find some big trout in the lake.